The present invention relates to improved particulates and methods of using such particulates in subterranean applications. More particularly, the present invention relates to high strength carbon foam particulates and their use in subterranean applications such as production enhancement and completion.
Particulates are used in a variety of operations and treatments performed in oil and gas wells. Such operations and treatments include, but are not limited to, production stimulation operations such as fracturing and well completion operations such as gravel packing and combinations operations such as frac-packing.
An example of a production stimulation operation using particulates is hydraulic fracturing. That is, a type of servicing fluid, referred to in the art as a fracturing fluid, is pumped through a well bore into a subterranean zone to be stimulated at a rate and pressure such that fractures are formed and extended into the subterranean zone. The fracture or fractures may be horizontal or vertical, with the latter usually predominating, and with the tendency toward vertical fractures increasing with the depth of the formation being fractured. The fracturing fluid is generally a gel, emulsion, or foam that comprises a particulate material often referred to as proppant. The proppant is deposited in the fracture and functions, inter alia, to hold the fracture open while maintaining conductive channels through which such produced fluids can flow upon completion of the fracturing treatment and release of the attendant hydraulic pressure.
An example of a well completion operation using particulates is gravel packing. Gravel packing treatments are used, inter alia, to reduce the migration of unconsolidated formation particulates into the well bore. In gravel packing operations, particles referred to in the art as gravel are carried to a well bore in a subterranean producing zone by a hydrocarbon or water carrier fluid. That is, the particulates are suspended in a carrier fluid, which may be viscosified, and the carrier fluid is pumped into a well bore in which the gravel pack is to be placed. As the particulates are placed in the zone, the carrier fluid leaks off into the subterranean zone and/or is returned to the surface. The resultant gravel pack acts as a filter to separate formation solids from produced fluids while permitting the produced fluids to flow into and through the well bore. While screenless gravel packing operations are becoming more common, traditional gravel pack operations involve placing a gravel pack screen in the well bore and packing the surrounding annulus between the screen and the well bore with gravel sized to prevent the passage of formation particulates through the pack with produced fluids. The gravel pack screen is generally a filter assembly used to support and retain the gravel placed during the gravel pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of a well bore, the production fluid, and any particulates in the subterranean formation. When installing the gravel pack, the gravel is carried to the formation in the form of a slurry by mixing the gravel with a viscosified carrier fluid. Once the gravel is placed in the well bore, the viscosity of the carrier fluid is reduced and it is returned to the surface. Such gravel packs are used to stabilize the formation while causing minimal impairment to well productivity. The gravel, inter alia, acts to the prevent the particulates from occluding the screen or migrating with the produced fluids, and the screen, inter alia, acts to prevent the gravel from entering the well bore.
In some situations the processes of hydraulic fracturing and gravel packing are combined into a single treatment to provide a stimulated production and an annular gravel pack to prevent formation sand production. Such treatments are often referred to as “frac pack” operations. In some cases the treatments are completed with a gravel pack screen assembly in place with the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In this situation the hydraulic fracturing treatment ends in a screen out condition creating an annular gravel pack between the screen and casing. This allows both the hydraulic fracturing treatment and gravel pack to be placed in a single operation. In other cases the fracturing treatment may be performed prior to installing the screen and placing a gravel pack.
Fracturing fluids, gravel packing carrier fluids and frac pack fluids generally must be highly viscous to be able to suspend particulates. To achieve a high viscosity, viscosifiers often are added to such fluids. Such viscosifiers are expensive. Moreover, as a fracture or a gravel pack is created a portion of the liquid contained in the fluid may leak off into the formation and/or may create an undesirable filter cake comprising deposited viscosifier on the walls of the fracture, well bore, or the formation.
Filter cakes are sometimes desirable to aid in preventing drilling and other servicing fluids from being lost in the formation and to prevent solids from entering the porosities of the producing formation. However, just as a filter cake may block the loss of fluids into the formation, the same filter cake may block the production of fluids from the formation. Thus, the presence of a filter cake on a producing zone is generally undesirable when a subterranean formation is returned to production. Moreover, residue of viscosifiers used in subterranean applications often remains on the particulates transported in the viscosified fluid and may reduce the conductivity of packs made from such particulates.
Also, as more wells are being drilled in deep water and in high temperature zones, gravel packing in long open horizontal well bores is becoming more prevalent. Completion operations in these wells generally involve the use of reduced-specific gravity particulates that are resistant to degradation in the presence of hostile conditions such as high temperatures and subterranean treatment chemicals. In order to prevent damage to these producing zones by gravel packing operations, the treating fluid carrying the particles should generally exhibit a relatively low viscosity by using low concentrations of gel polymers. Similarly, fracture stimulation treatments carried out in deep, high temperature wells may require similar reduced-specific gravity particles suspending in lower viscosity fluids.
Traditional high-strength particulates used in subterranean applications often exhibit too high of a specific gravity to be suspended in such lower viscosity fluids. While low specific gravity particulates, such as walnut hulls are well known in the art, generally they are not able to withstand significant closure stresses over time at elevated subterranean temperatures. Similarly, a variety of lightweight particles formed of thermoplastic materials including polyolefins, polystyrene divinylbenzene, polyfluorocarbons, polyethers, etherketones, and polyamide imides are commercially available. However, when these particles are exposed to temperatures above about 150° F., they soften and deform, and are not suitable in all well bores.